Originally Posted by Distill

The opacity limit will depend on your printer. I've had problems in the past where something I'd intended to be very subtle ended up being darker just because the smallest dot the printer could make was too big. It ended up being a few widely-spaced but definite specks (far from the look it had on screen).

Your best bet is to test it (if you're printing yourself) or to get a proof (if sending it out to a printer). A pain in the butt either way.

Anyone else have a good rule of thumb?